Hog manure treatment system

ABSTRACT

The invention relates to a method of treating manure such that odour from the manure is significantly reduced or eliminated and producing therefrom recyclable water, value-added biosolids and ammonia. Specifically, the manure is combined with lime at high pH. The material is mixed under negative pressure and the basic conditions cause ammonia to be evolved from the manure which is then drawn off and recovered. A coagulating agent is then added which further promotes floc formation within the manure. Following further mixing, flocs are separated from the liquid portion. A struvite-promoting chemical and a coagulant are then added to the liquid portion which causes further floc formation, and the flocs are again separated from the substantially clear liquid. It is of note that as a result of this process, the solids are highly hydrophobic and dry very quickly. It is of further note that solids isolated from either step can be combined and sold, for example, as fertilizer, as discussed below. The clear liquid can be used, for example, in barn washes or for horticultural watering.

FIELD OF THE INVENTION

The present invention relates generally to the field of waste treatment.More specifically, the present invention relates to a system and amethod for treating manure.

BACKGROUND OF THE INVENTION

According to municipalities, government agencies, environmentalists andthe public in general, odour and potential pollution sources emanatingfrom livestock, for example, hog, dairy, feedlot and chicken, facilitiesare the main issues that the livestock industry needs to address inorder to sustain its development. The most intense source of odour fromlivestock facilities occurs during manure handling and land application.

U.S. Pat. No. 1,915,240 teaches a sewage purification method whichcomprises mixing lime and ferric chloride with raw sewage, whichdeodorizes the waste and causes floc formation. The floc is thenoxidized and sterilized before being allowed to settle for subsequentremoval and dewatering.

U.S. Pat. Nos. 3,619,420 and 3,640,820 teach a sewage treatment processwherein treated sludge is converted to an active substance by heattreatment and returned to the sewage treatment tank, thereby improvingthe operational efficiency of the method.

U.S. Pat. No. 4,309,291 teaches a method of continuous flow flocculationand clarification wherein waste water is flocculated by subjecting themixture to continuous, turbulent flow to and from a settling tank.Clarified effluent and settled flocculent are continuously dischargedfrom the settling tank.

U.S. Pat. No. 4,111,800 teaches a process for treating municipal solidwaste and raw sewage sludge wherein municipal waste is mixed withcellulose-containing solid waste.

U.S. Pat. No. 4,180,459 teaches a process of making agriculturalproducts from organic sewage sludge comprising treating sewage sludgewith FeCl₃ and CaO from various sources, preferably from sugar refiningfor flocculation. It is of note that the sewage sludge is characterizedas “acidic conditioned sludge” having a pH of between 3.0-5.7.

U.S. Pat. No. 4,209,393 teaches using coal as a sewage sludge additiverather than activated carbon.

U.S. Pat. No. 4,212,732 teaches a raw liquid waste treatment processwherein ash and activated carbon are added to raw sewage to promotesettling of flocculent.

U.S. Pat. No. 4,670,158 teaches a method of wastewater treatment whereinlime and phosphoric acid are added to wastewater to promoteflocculation. In this method, the pH of the wastewater is adjusted to bewithin 7.0-10.0, preferably 8.5-9.0 with phosphoric acid.

U.S. Pat. No. 5,698,110 teaches a deodorizing composition for treatinganimal waste comprising a mixture of lime and cellulose so that thewaste can subsequently be used as fertilizer.

U.S. Pat. No. 5,897,785 teaches a process for treating animal wastewherein waste is diluted with water and exposed to radiation toeliminate pathogens. High charge, cationic polymers are then added tothe waste such that polymerized solids are formed which are thenseparated from the waste.

U.S. Pat. No. 5,958,758 teaches a process for treating animal wastewherein sulfide-utilizing bacteria are added to the waste followed bythe addition of organic digesting bacteria and lytic enzymes.

U.S. Pat. No. 6,033,570 teaches a process for the treatment of liquidhog manure in which cellulosic material is added to promote removal ofsolids from the liquid.

U.S. Pat. Nos. 6,039,875 and 6,214,230 teach the use ofbacterially-generated polymers as coagulants for the removal ofsuspended solids from wastewater.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a methodof treating manure comprising:

a) mixing a quantity of manure with lime such that said mixture has abasic pH;

b) adding a first coagulating polymer to said mixture, thereby promotingfloc formation within said mixture;

c) separating the floc from the mixture, thereby forming solids and aliquid portion;

d) adding a second coagulating polymer and/or a struvite-promotingcompound to said liquid portion, thereby forming solids and clearliquid; and

e) separating the clear liquid from the solids.

According to a second aspect of the invention, there is provided the useof SUPERFLOC as a coagulant in manure treatment.

According to a third aspect of the invention, there is provided acomposition for promoting struvite formation comprising a struvitepromoting compound and a coagulating polymer.

According to a fourth aspect of the invention, there is provided amethod of promoting struvite formation comprising:

providing a quantity of liquid containing dissolved phosphorous;

adding a struvite promoting compound and a coagulating polymer to saidliquid, thereby forming a mixture;

mixing said mixture, thereby promoting struvite formation;

allowing said mixture to stand, thereby separating said mixture intostruvite and clear liquid; and

separating the struvite and the clear liquid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic drawing of the method.

FIG. 2 shows a schematic drawing of an alternate embodiment of themethod.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the invention belongs. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, the preferred methodsand materials are now described. All publications mentioned hereunderare incorporated herein by reference.

Described herein is a method or process of treating manure comprising:

a) mixing a quantity of manure with lime such that said mixture has abasic pH;

b) adding a first coagulant to said mixture, thereby promoting flocformation within said mixture;

c) separating the floc from the mixture, thereby forming solids and aliquid portion;

d) adding a second coagulant and a struvite-promoting compound to saidliquid portion, thereby forming solids and clear liquid; and

e) separating the clear liquid from the solids.

The invention relates to a method of and a process for treating manuresuch that odour from the manure is significantly reduced or eliminatedand producing therefrom recyclable water, value-added biosolids andammonia. Specifically, the manure is combined with lime, resulting in amixture having a basic pH. The basic conditions cause gases, forexample, ammonia to be evolved from the manure, so the mixture is mixedunder negative pressure and the gases are drawn off and recovered, asdescribed below As a result of this treatment, the manure is deodorizedand sterilized as pathogens are unable to survive at the high pH. Acoagulating agent is then added which further promotes floc formationwithin the manure. Following further mixing, the flocs are separatedfrom the liquid portion. A struvite-promoting chemical and a coagulantare then added to the liquid portion which causes further flocformation, and the flocs are again separated from the now substantiallyclear liquid. It is of note that as a result of this process, the solidsare highly hydrophobic and dry very quickly. It is of further note thatsolids isolated from either step can be combined and used, for example,as fertilizer, as discussed below. The clear liquid can be used, forexample, for barn washing or for horticultural watering.

The invention will now be described in detail by examples, although theinvention is not limited to the examples.

In the exemplary examples, the manure is hog manure. However, as will beappreciated by one knowledgeable in the art, other types of manure, forexample, manure from dairy or feedlot animals or chickens as well as,for example, septage from sewage holding tanks or effluent fromrendering (abattoir) plants, may also be used in the invention.

Referring to FIG. 1, manure from a barn 10 is collected, for example, ina manure pit 12 beneath the barn 10 and is transferred to a holding tank14. Lime, for example, hydrated lime or unhydrated lime (Ca(OH)₂) isadded to the manure and the manure is mixed vigorously (for example, 100rpm) for several hours, in some embodiments, 10-12 hours, although othersuitable time periods may be used according to the conditions of themanure and desired results. In some embodiments, lime is added at dosingrates ranging from less than 5 g/l to about 20 g/l. As a result of theaddition of the lime, the pH in the manure is raised to above 11.0, morepreferably to above 11.5 and yet more preferably to 12.0-12.5. This inturn causes small flocs to develop within the manure and alsovolatilizes gases, for example, ammonia within the manure. It is of notethat some of the other dissolved gases, for example, skatoles andmercaptans, may also be volatilized in smaller quantities. In someembodiments, the holding tank 14 is kept under negative pressure andevolved gases are removed from the holding tank 14. Specifically, thegases are removed via pipes 15 and then bubbled through low pH water 16.As will be apparent to one knowledgeable in the art, the ammonia readilydissolves into the water and is thereby recovered.

It is of note that in some embodiments, NaOH or other suitable chemicalsmay be added first to raise the pH followed by the addition of Ca(OH)₂to generate flocs.

Thus, addition of the lime at a high pH both deodorizes and sterilizesthe manure, as pathogens are unable to survive at the high pH.Furthermore, as discussed above, the addition of the lime results insome floc formation.

The manure mixture is then transferred to a first reaction tank 18wherein the mixing speed is reduced to less than 20 rpm and a firstcoagulating agent is added. In one embodiment, the first coagulatingagent is a flocculating or coagulating polymer known in the art, ofanionic, cationic or non-ionic type, or a combination of such polymersand polyacrylamides. These coagulating and flocculating agents known inthe art are currently used in the flocculation of sewage and otherindustrial and agricultural effluents. Many of these agents are polymersand/or inorganic chemicals. As will be appreciated by one knowledgeablein the art, examples of coagulating polymers include but are by no meanslimited to, for example SUPERFLOC, manufactured by CYTEC, alum, WEB-3 orWEB1500. It is of note that other suitable coagulants may also be used.The polymer may be added in a gentle stream, as shown at 20 in FIGS. 1and 2. As will be apparent to one knowledgeable in the art, SUPERFLOC isviscous and addition thereof must be controlled for optimal results.However, other suitable means known in the art of adding the coagulatingagent so that good mixing within the manure mixture is obtained may alsobe used. As will be appreciated by one knowledgeable in the art,SUPERFLOC dosage is determined by the chemical characteristics of themanure to be treated. In some embodiments, the dosing rates can varyfrom 2 ml per litre to more than 10 ml per litre. SUPERFLOC is asolution of SUPERFLOC powder in water. It is preferably a 0.25% to 1%solution of SUPERFLOC powder in water. Producing a solution of higherconcentration may be limited by the high viscosity of the resultingproduct.

The manure is mixed at the low mixing speed until large flocs developand the manure slurry increases in viscosity, in some embodiments, for10-15 minutes. Specifically, the slurry is mixed until flocs becomestable and a layer of clear liquid begins to form at the top. At thispoint, the slurry is allowed to settle into solids and a liquid portion.In some embodiments, the slurry may be transferred to a settling tank19, as shown in FIG. 1.

As can be seen in FIGS. 1 and 2, settleable solids may be removed fromthe bottom of the reaction and settling tanks, as discussed below.

The slurry is then passed through a screening device to separate thesolids from the liquid portion. Specifically, the solids are removedand/or separated in a mechanical/settling process and the liquid isdecanted to the second reaction tank 20. The liquid portion resultingfrom this stage of treatment is turbid but mostly devoid of anysettleable solids fraction and is passed to the second reaction tank.

The liquid portion in the second reaction tank 20 is mixed with astruvite-promoting compound, for example, MgCl₂, MgSO₄, MgCO₃ ormagnesium oxide or a coagulant polymer as described above, orcombinations thereof. In one embodiment, MgCl₂, either as a hydrate(MgCl₂:6H₂O) or in the anhydrous form is added. At this stage, a secondcoagulant is also added. In some embodiments, the second coagulant isSUPERFLOC, which is again added in a gentle stream, as discussed above.It is of note that in addition to or in place of SUPERFLOC, othercoagulants may also be used. These include coagulant and flocculentagents known in the art and currently used in the flocculation of sewageand other industrial and agricultural effluents. Many of these agentsare polymers and/or inorganic chemicals. When MgCl₂, in someembodiments, at 1 g per litre to 10 g per litre depending upon thechemical characteristics of the manure, and SUPERFLOC, in someembodiments, at less than 2 ml per litre to more than 10 ml per litredepending upon the chemical characteristics of the manure, are added tothis liquid with continuous mixing, large flocs begin to form due to theformation of struvite, a magnesium-phosphorous compound, which is highlyinsoluble in water Thus, this combination of coagulant andstruvite-promoting compound has the surprising effect of promoting flocformation to a great extent so that the flocs begin to get denser andprecipitate to the bottom. After standing, the liquid portion is againpassed through a screening device to separate the settled solids fromthe liquid portion. Specifically, the solids are removed and/orseparated in a mechanical/settling process and the liquid is decanted tothe next tank. It is of note that a clear liquid is obtained from thisstage of treatment. It is also of note that the liquid may be treated asecond time with the struvite-promoting compound(s) as described above,and as shown in FIG. 1 wherein the third reaction tank is shown as 22.As will be appreciated by one of skill in the art, the necessity of thisadditional step will depend on the effluent being treated.

The solids from the tanks are collected and spread to dry, as showngenerally in FIGS. 1 and 2 as 24. As discussed above, as a result oftreatment, the solids develop a hydrophobic tendency and allow the waterto drain away naturally leaving dry solids behind. Furthermore, thesolids dry very quickly as a result of this hydrophobicity.

The dried solids can be used as, for example, fertilizer. It is also ofnote that the dried solids have high heating value (calorific value),equal to or higher than the calorific value of lignite coal. As aconsequence, the solids may be used as a heating fuel in boilers orfurnaces. It is of note that, as discussed above, as a result of theprocess, the solids dry quickly and are substantially odor-free andpathogen-free.

The liquid portion is removed from the last tank, shown generally at 26and can be used for example, for horticultural watering, for example,crops or trees, or for barn washing. It is of note that followingtreatment by the process, the liquid portion is ready for immediate useand does not require further settling or treatment. However, dependingon the effluent, in some embodiments, the liquid may be pumped through afilter media, for example, activated carbon, sand or a combinationthereof in a tank.

It is of note that in the process described above, the dosing techniquesused to add the reactants may include in-line injection, spraying,atomizing or any other type of method used for chemical injection knownin the art. It is of note that the reactants may be added separately ormay be mixed prior to injection.

As will be appreciated, the operating configuration of the treatmentprocess as shown in FIG. 1 is for illustrative purposes only. It is ofnote that many modifications and variations are possible to suitsite-specific requirements. For example, the number of tanks and therelated hardware may be modified. Thus, the invention is not restrictedto the operation shown in the figures. It is also of note that thetreatment process can be operated without the second stage of treatmentfor producing recyclable, clear water. It is of further note that thetwo stages can be repeated either individually or in variouscombinations to provide the desired or required final product.

While the preferred embodiments of the invention have been describedabove, it will be recognized and understood that various modificationsmay be made therein, and the appended claims are intended to cover allsuch modifications which may fall within the spirit and scope of theinvention.

1. A method of treating manure comprising: a) mixing a quantity ofmanure with lime such that said mixture has a basic pH; b) adding afirst coagulating polymer to said mixture, thereby promoting flocformation within said mixture; c) separating the floc from the mixture,thereby forming solids and a liquid portion; d) adding a secondcoagulating polymer and/or a struvite-promoting compound to said liquidportion, thereby forming solids and clear liquid; and e) separating theclear liquid from the solids.
 2. The method according to claim 1 whereinthe manure is selected from the group consisting of hog manure, feedlotmanure, dairy cow manure and chicken manure.
 3. The method according toclaim 1 wherein the basic pH is a pH above
 11. 4. The method accordingto claim 1 wherein the basic pH is a pH above 11.5
 5. The methodaccording to claim 1 wherein the basic pH is between 11.5-12.5.
 6. Themethod according to claim 1 including removing evolved ammonia duringstep (a).
 7. The method according to claim 6 wherein the ammonia isremoved by bubbling the evolved ammonia into water.
 8. The methodaccording to claim 1 wherein the first coagulating polymer is selectedfrom the group consisting of alum and SUPERFLOC.
 9. The method accordingto claim 1 wherein the second coagulating polymer is selected from thegroup consisting of alum and SUPERFLOC.
 10. The method according toclaim 1 wherein the struvite-promoting compound is selected from thegroup consisting of MgCl₂, MgSO₄, MgCO₃ and magnesium oxide.
 11. Use ofSUPERFLOC as a coagulant in manure treatment.
 12. A composition forpromoting struvite formation comprising a struvite promoting compoundand a coagulating polymer.
 13. The composition according to claim 12wherein the struvite promoting compound is selected from the groupconsisting of MgCl₂, MgSO₄, MgCO₃ and magnesium oxide.
 14. Thecomposition according to claim 12 wherein the coagulating polymer isselected from the group consisting of alum and SUPERFLOC.
 15. A methodof promoting struvite formation comprising: providing a quantity ofliquid containing dissolved phosphorous; adding a struvite promotingcompound and a coagulating polymer to said liquid, thereby forming amixture; mixing said mixture, thereby promoting struvite formation;allowing said mixture to stand, thereby separating said mixture intostruvite and clear liquid; and separating the struvite and the clearliquid.
 16. The method according to claim 15 wherein the struvitepromoting compound is selected from the group consisting of MgCl₂,MgSO₄, MgCO₃ and magnesium oxide.
 17. The method according to claim 15wherein the coagulant is selected from the group consisting of alum andSUPERFLOC.